1. Field of the Invention
The present invention relates to an image display technique.
2. Description of the Related Art
A liquid crystal display apparatus (for example, direct view type liquid crystal display apparatus or liquid crystal projector) adjusts the quantity of light always emitted by a light source using a liquid crystal shutter, and is called a hold type display apparatus. The hold type display apparatus emits light in one frame period.
To improve the moving image quality in a liquid crystal display apparatus using a reflective liquid crystal, it is necessary that transition of the liquid crystal is completed within one frame period and the reflectance of every frame reaches a predetermined one. However, at a low liquid crystal response speed, the transition of the liquid crystal is not completed within one frame period, failing in display at a predetermined reflectance. To increase the liquid crystal response speed, there is proposed a method of comparing a video signal to be displayed in the current frame with one displayed in an immediately preceding frame, correcting the video signal to be displayed in the current frame in accordance with the comparison result, and driving the liquid crystal display (patent literature 1 (Japanese Patent No. 3305240)). This method is a so-called overdrive method.
However, the overdrive method has a problem that no desired correction can be done near the maximum and minimum gray levels and the reflectance cannot reach a predetermined one. The vicinity of the maximum gray level will be exemplified. Assume that an immediately preceding frame has a gray level of 240 (8 bits), the current frame has a gray level of 255 (8 bits), and the amount of correction by the overdrive method is 16 (8 bits). In this case, the current frame has the gray level of 255 (8 bits), so no more correction can be performed in the positive direction. As a result, the current frame cannot obtain a reflectance corresponding to the gray level of 255 (8 bits).
To solve this problem, patent literature 2 (Japanese Patent Laid-Open No. 2004-246312) discloses the following technique. More specifically, patent literature 2 discloses a technique of, when a predetermined reflectance cannot be obtained in the current frame, predicting the ultimate reflectance, and calculating an overdrive value in the next frame from the predicted ultimate reflectance to prevent the influence on the next frame.
However, the technique in patent literature 2 prevents the influence of a failure to obtain a predetermined reflectance on the next frame, but is not intended to make the liquid crystal accurately reach reflectances corresponding to the maximum and minimum gray levels.